The invention relates to treating effluent gas containing polycyclic aromatic hydrocarbons.
The field of application of the invention is more particularly that of treating effluent gas produced by industrial installations for chemical vapor deposition or infiltration to form a deposit of pyrolytic carbon on substrates or to densify porous substrates with a matrix of pyrolytic carbon.
Such installations are very well known. Substrates for coating or densifying with pyrolytic carbon are placed in an oven into which a reagent gas containing one or more precursors of said carbon is introduced. The precursor gas is a hydrocarbon, typically methane, propane, or a mixture of both. The pressure and the temperature in the oven are adjusted so as to cause the coating or the matrix of pyrolytic carbon to be produced by the precursor gas decomposing (cracking) on coming into contact with the substrates. The effluent gas containing by-products of the reaction is extracted continuously from the oven by pumping.
The by-products of the reaction comprise organic compounds having a very high solidification temperature, in particular polycyclic aromatic hydrocarbons (PAHs) such as, in particular: naphthalene, pyrene, anthracene, acenaphthylene, . . . . On condensing, these reaction by-products form tars which tend to become deposited in the outlet pipework from the oven as the effluent gas cools. These tars are also to be found in the pumping apparatus, e.g. in the oil of vacuum pumps or in condensates from steam ejectors.
Similar problems can be encountered with industrial installations other than ovens for chemical vapor deposition or infiltration but that also make use of hydrocarbons as reagent gas, for example cementation ovens.